1. Field of the Invention
The present invention relates to a nonvolatile memory, and more particularly, to a nonvolatile memory having a reprogramming function.
2. Description of the Related Art
FIG. 1 schematically shows a flow chart illustrating a conventional method for fabricating a nonvolatile memory. Referring to FIG. 1, a plurality of steps are required for fabricating a nonvolatile memory. First, in step S101, the fabrication process is performed. Then, in step S103, a test process is performed on the nonvolatile memory. When the test result is indicated that the nonvolatile memory is good (i.e. “good” as indicated in step S103), a packaging process is performed in step S11. Otherwise, if it is found that a defect exists in the nonvolatile memory during the fabrication process of S101 (i.e. “fail” as indicated in step S103), an E-fuse technique is performed to repair the nonvolatile memory during step S105. In step S107, the fabrication process is performed. Then in step S109, the testing process is performed on the repaired nonvolatile memory. If the repaired nonvolatile memory is made to be a good product (i.e. “good” as indicated in step S109), the packaging process is performed in step S111. However, if there is still some defects in the repaired nonvolatile memory (i.e. “fail” as indicated in step S103), the nonvolatile memory is scrapped.
Referring to FIG. 1, after the packaging process is completed on the nonvolatile memory, a program code is recorded into the memory in step S113, and a final testing is performed in step S115. Then, in step S117, it is determined whether the memory has passed the final testing of step S115. If the memory has passed the final testing in step S115 (i.e. “yes” as indicated in step S117), a final testing is directly performed on the memory in step S121. Otherwise, if the memory does not pass the final testing in step S115 (i.e. “no” as indicated in step S117), the E-fuse technique is performed to repair the nonvolatile memory in step S119. Then the final testing is performed again on the memory in step S121. Afterwards, in step S123, it is determined whether the memory has passed the final testing in step S121. If the memory does not pass the final testing in step S121 (i.e. “no” as indicated in step S123), the memory is scrapped. Otherwise, if the memory has passed the final test of step S121 (i.e. “yes” as indicated in step S123), the memory is ready for shipment.
In general, the final testing in the steps S115 or S121 mentioned above may include a temperature test, that is to test the operation of the memory under different temperature environments. In such cases, various thermal intensities having different temperatures are applied on the memory. However, the charges inside the memory are easily lost under exposure to elevated temperatures. And the program code could be messed up if the memory is used for an extended period of time under such elevated temperature conditions. Accordingly, a nonvolatile memory having a self-refreshing function is disclosed in U.S. Pat. No. 5,347,486.
The technique disclosed in U.S. Pat. No. 5,347,486 is suitable for larger capacity memory devices. Since its circuit structure is more complicated, it is not as suitable for application in the smaller sized circuit. However, micro circuit is widely used in different applications such as the RFID (radio frequency identification) circuit where the memory device disclosed in U.S. Pat. No. 5,347,486 is not as suitable.